One of ordinary skill in the art knows well the problems associated with the repeated administrations of drugs. Apart from the troubles and discomforts, mostly psychological, which the patient can experience when he has to remember to take, that determinate medicine three or four times a day (as it happens, for instance, with paracetamol), it must be borne in mind that, from the point of view of absorption kinetics, repeated administration is responsible for very high hematic levels of the drug which repeatedly occur in the organism of the patient, with a remarkable increase in the possibility of side effects. In the literature many methodologies are described, generically called "retard", by means of which the number of repeated administrations of a drug can be reduced while still keeping unaltered its therapeutic effectiveness in time.
Thus, for instance, slow-release tablets of indomethacin, in which the active principle is coated by a film of a hydrophilous polymer and by a cellulose ether, are disclosed in Japanese laid open application J 58170712, while in Japanese laid open application J 59084821, diclofenac, which is another well known antiphlogistic agent, is mixed with .beta.-cyclodestrin. In German laid open application DE 3001797, indoprofen, a good analgesic and antiinflammatory agent which has the drawback of having a short plasmatic half-life, is microencapsulated in a protective layer of a cellulose ether, thus obtaining a remarkable improvement of its plasmatic half-life. Finally, in European publications EP 0094116, EP 0094117 and EP 0094123, granules are described which have a double coating; the first one is made by polyvinylpyrrolidone and the second one is made by acrylic polymers or by cellulose esters or by fatty or oily substances, which should allow a better release of antiphlogistic drugs either in the stomach and in the intestine.
In all of these galenic formulations, however, the initial release of the active ingredient is gradual and slow, so that the therapeutic effect begins only several hours after the administration. This is an evident drawback, especially in the case of drugs which contemporaneously present anti-inflammatory, analgesic and antipyretic activity, in which often a quick release is needed to obtain a prompt analgesic effect, besides the slow and regular release in order to cure the inflammation.